#include<bits/stdc++.h>
#define VAR(i,n) __typeof(n) i = (n)
#define loop(i,j,s) for(int i=j;i<s;i++)
#define loopback(i,j,s) for(int i=j;i>=s;i--)
#define foreach(i,c) for(VAR(i,(c).begin());i!=(c).end();i++)
#define pln( x ) cout << x << "\n"
#define ps( x ) cout << x << " "
#define entr cout << "\n"
#define pcnt(i) __builtin_popcount(i)
#define ll long long
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define SIZE(c) (c).size()
#define ALL(c) (c).begin(), (c).end()
using namespace std;
typedef vector<ll> vi;
typedef pair<ll,ll> pii;
typedef vector<vector<int> > VVI;
const int INFTY=20000000;
const int MAX=500100;
const ll MOD=1000000007;
void coutTab(int* tab,int n){
loop(i,0,n){
cout<<tab[i]<<" ";
}
cout<<"\n";
}
template<class T> void coutVec(vector<T> tab){
for(T t : tab){
cout<<t<<" ";
}
cout<<"\n";
}
//------------------------------------------
void solve(int n, vi a) {
vi dp(n);
ll e=0,o=0;
if(a[0]%2 == 0) e = 1;
else o = 1;
dp[0] = e;
loop(i,1,n) {
if(a[i]%2 == 0) {
e = (e + dp[i-1])%MOD;
} else {
swap(e,o);
o = (o + dp[i-1])%MOD;
}
dp[i] = e;
//pln(dp[i]);
}
pln(dp[n-1]);
}
void solve_brute(int n, vi a) {
vi dp(n);
dp[0] = (a[0]%2==0);
loop(i,1,n) {
ll S=a[i];
loopback(j,i-1,0) {
if(S%2==0) dp[i] = (dp[i] + dp[j])%MOD;
S = (S+a[j])%MOD;
}
if(S%2==0) dp[i] = (dp[i] + 1)%MOD;
//pln(dp[i]);
}
pln(dp[n-1]);
}
int main(){
ios_base::sync_with_stdio(0);
int n;
cin>>n;
vi a(n);
loop(i,0,n) cin>>a[i];
if(n < 5000) solve_brute(n, a);
else solve(n,a);
}
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 | #include<bits/stdc++.h> #define VAR(i,n) __typeof(n) i = (n) #define loop(i,j,s) for(int i=j;i<s;i++) #define loopback(i,j,s) for(int i=j;i>=s;i--) #define foreach(i,c) for(VAR(i,(c).begin());i!=(c).end();i++) #define pln( x ) cout << x << "\n" #define ps( x ) cout << x << " " #define entr cout << "\n" #define pcnt(i) __builtin_popcount(i) #define ll long long #define pb push_back #define mp make_pair #define ff first #define ss second #define SIZE(c) (c).size() #define ALL(c) (c).begin(), (c).end() using namespace std; typedef vector<ll> vi; typedef pair<ll,ll> pii; typedef vector<vector<int> > VVI; const int INFTY=20000000; const int MAX=500100; const ll MOD=1000000007; void coutTab(int* tab,int n){ loop(i,0,n){ cout<<tab[i]<<" "; } cout<<"\n"; } template<class T> void coutVec(vector<T> tab){ for(T t : tab){ cout<<t<<" "; } cout<<"\n"; } //------------------------------------------ void solve(int n, vi a) { vi dp(n); ll e=0,o=0; if(a[0]%2 == 0) e = 1; else o = 1; dp[0] = e; loop(i,1,n) { if(a[i]%2 == 0) { e = (e + dp[i-1])%MOD; } else { swap(e,o); o = (o + dp[i-1])%MOD; } dp[i] = e; //pln(dp[i]); } pln(dp[n-1]); } void solve_brute(int n, vi a) { vi dp(n); dp[0] = (a[0]%2==0); loop(i,1,n) { ll S=a[i]; loopback(j,i-1,0) { if(S%2==0) dp[i] = (dp[i] + dp[j])%MOD; S = (S+a[j])%MOD; } if(S%2==0) dp[i] = (dp[i] + 1)%MOD; //pln(dp[i]); } pln(dp[n-1]); } int main(){ ios_base::sync_with_stdio(0); int n; cin>>n; vi a(n); loop(i,0,n) cin>>a[i]; if(n < 5000) solve_brute(n, a); else solve(n,a); } |
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